Pharmaceutically active molecules such as proteins and polypeptides have been conjugated with polydispersed mixtures of polyethylene glycol or polydispersed mixtures of polyethylene glycol containing polymers to provide polydispersed mixtures of drug-oligomer conjugates. For example, U.S. Pat. No. 4,179,337 to Davis et al. proposes conjugating polypeptides such as insulin with various polyethylene glycols such as MPEG-1900 and MPEG-5000 supplied by Union Carbide.
U.S. Pat. No. 5,567,422 to Greenwald proposes the conjugation of biologically active nucleophiles with polyethylene glycols such as m-PEG-OH (Union Carbide), which has a number average molecular weight of 5,000 Daltons.
U.S. Pat. No. 5,405,877 to Greenwald et al. proposes reacting bovine hemoglobin with thiazolidine thione activated PEG, which was prepared using m-PEG carboxylic acid having a number average molecular weight of 5,000 Daltons.
U.S. Pat. No. 5,359,030 to Ekwuribe proposes conjugating polypeptides such as insulin with polyethylene glycol modified glycolipid polymers and polyethylene glycol modified fatty acid polymers. In this patent, the number average molecular weight of polymer resulting from each combination is preferred to be in the range of from about 500 to about 10,000 Daltons.
PEG is typically produced by base-catalyzed ring-opening polymerization of ethylene oxide. The reaction is initiated by adding ethylene oxide to ethylene glycol, with potassium hydroxide as catalyst. This process results in a polydispersed mixture of polyethylene glycol polymers having a number average molecular weight within a given range of molecular weights. For example, PEG products offered by Sigma-Aldrich of Milwaukee, Wis. are provided in polydispersed mixtures such as PEG 400 (Mn 380-420); PEG 1,000 (Mn 950-1,050); PEG 1,500 (Mn 1,400-1,600); and PEG 2,000 (Mn 1,900-2,200).
It is desirable to provide non-polydispersed mixtures of drug-oligomer conjugates that comprises polyalkylene glycol.